Integral membrane proteins perform important communication and transport functions at the cell membrane. These proteins can and do exist as multiple peptide complexes or oligomers. In analogy to the soluble enzyme complexes, the multiple peptide complexes are expected to exhibit distinct functional properties. To further our understanding of the dynamic states of protein in membrane we must be able to quantitatively measure the degree of interaction and to determine the functional properties of the complexes formed. This project proposes to study the distribution of protein-protein complexes in membranes and the functional properties of these complexes. The integral proteins to be studied are the well characterized acetylcholine receptor and (Na ion, K ion)-ATPase. These proteins have clearly defined functions which are modulated by the cell. The mechanism of modulation and the oligomeric protein states in the membrane remain to be determined. This project will use calibrated nonradiative energy coupling to identify the oligomeric state of the proteins in reconstituted bilayers. It will use planar bilayer techniques to monitor function of the identified protein complexes.